Short-wave amplifier



Oct. 3-,1944.

P. F. BYRNE SHORT WAVE AMPLIFIER Original Filed March 22, 1939 NSN INVENTOR.

ATToRyEY.

Patented Oct. 3, 1944 SHORT-WAVE AMPLIFIER Paul F. Byrne, West Caldwell, N. J., assignor to Federal Telephone and Radio Corporation, a

corporation of Delaware Original application March 22, 1939, Serial No. 263,367. Divided and this application November 28, 1941, Serial No. 420,794

2 Claims.

My invention relates to high frequency transmission systems and more particularly to radio frequency transmission circuits-adapted to supply energy to two or more symmetrical loads from an unsymmetrical source of supply or from a single symmetrical two conductor line or loop. This invention is a division of my copending application Serial No. 263,367, filed March 22, 1939, and entitled (Short-wave transmitters, issued on June 9, 1942, as Patent No. 2,285,851.

It is often desirable to transmit energy from an unsymmetrical source such as an oscillator or frequency multiplier grounded on one side, to two or more symmetrical loads, for example, radiating antennae. This type of arrangement isparticularly useful for supplying energy to transmitting antennae which may be usedfor defining a beacon course, since under these circumstances it is desirable that the load be properly balanced in order that the system be efilcient and a suitable radiation pattern be secured. Furthermore, in beacon systems it is often desired to separately adjust the power fed to each of the radiating antennae, so that the course line may be properly defined and maintained. Similarly it may be desired to connect two or'more balanced lines over which energy is transmitted to a single unbalanced line or to a single balanced line.

It is an object of my invention to provide a radio frequency transmission system which is suitable for intercoupling two or more balanced lines and an unbalanced line.

It is a further object of my invention to provide a radio transmitter in which energy from an unbalanced source is applied to a plurality oi antennae each connected to a separate balanced line.

It is a further object of my invention to provide in a radio transmitter a system which permits the independent adjustment of energy to the separate balanced-antennae.

It is a still further object of my invention to provide the combination of a radio frequency source, a balanced amplifier and a plurality of balanced loads connected to the output of the amplifier.

It is a still further object of my invention to provide a radio transmitter with a balanced line 7 objects of my invention and the manner of attaining them will be apparent from a particular description of my invention'made in accordance with the accompanying drawing, in which Fig. 1 illustrates a preferred embodiment of a radio transmitter made in accordance with my invention,

Fig. 2 illustrates a form of split stator condenser suitable for use in the modulation system of Fig. 1, and

Fig. 3 illustrates an alternative modulation system in accordance with my invention which may beused in place of that disclosed in Fig. 1.

Turning now to the drawingand particularly to Fig. 1, I00 represents a source of radio frequency energy which may be, for example, an 0'scillator or a frequency multiplier. In source I00 at I02 is indicated a vacuum tube which may mp resent the last stage of the radio frequency circuit within I00. The anode of tube I02 is connected to a positive voltage. supply as indicated. and is connectedthrough the primary of transformer I03 to ground for radio frequencies through the radio frequency condenser IOI. Transformer I03 is designed for high frequencies and constitutes a single turn for the primary and secondary so that the coupling between the primary and secondary is made by means of a distributed inductance and capacity only. Coupling transformer I03 is made adjustable so that the coupling between the windings may be varied.

The secondary of the transformer I03 isconnected to ground on one side and on the other side to a transmission line I04, through a variable power controlling condenser I05. It is evident that this arrangement forms an unsymmetrical line portion. This unsymmetrical line is connected to a push-pull amplifier comprising vacuum tubes I08, I01. Since, in order for the vacuum tubes to operate properly in push-pull the 7 input thereto should be balanced, I provide a network to achieve this balance indicated generally at I00. At lower ratio frequencies balanced input may be obtained by merely grounding the center point of a transformer and connecting the outer ends through lines to the grid. However, at higher frequencies balance cannot be obta'ne'd so simply. A balance may be obtained by connecting in series across the line a pairof impedances such as 0, III, and connecting these impedances to ground through a third impedance H2. In the circuit shown in Fig. 1, impedances H0 and III areinductances, whereas impedance III is a condenser. A balance may be obtained in this way provided impedances H0, and III are properly related to impedance 6 ii. in value and are of a sign opposite to that of I it. In the preferred arrangement impedances lid and iii are made equal and impedance H2 is made equal to one-half the value of either of the impedances i it, or Iii. However, a considerable departure from this relationship may occur in practice, approximate equality of impedances lid and iii being sufilcient, and a. considerable variation in the relationship of the impedance values of H2 and H9, HI being permissible for most applications. In order that a complete balance may be obtained inductances iId and iii are arranged so as to have very little, if any, mutual coupling between them. IA blocking condenser lid is provided between inductance Ill and the junction points of Hill and M2, so that grid bias power may be supplied to the grid of tubes lot and 6 ill through the leads lid, lid independently of each other. This arrangement permits the use of separate grid meters to indicate the operation of the tubes. The output circuit of the vacuum tubes 66S, Iill, is connected to a high frequency variable transformer its, the primary of which is connected to a power supply through radio frequency choke H6. Tuning condensers till are provided to tune the output of push-pull amplifier. Cou= pied to the secondary of transformer t id are condoctors I I8, lit, which together form a balanced output line. The separate conductors Ila, IIII, are unbalanced with respect to ground so that each conductor may be considered as a further unsymmetrical line. The midpoint of the secondery of transformer lid is grounded so that in effect each of lines H8 and I I9 may be considered as an independent unbalanced line with a ground return. In lines .I I8, H9, are provided variable condensers no, I2I which may serve to independently control the power output over the respective lines.

In line H8 is provided another high frequency network which serves to-produce a balanced output from the unsymmetrical line H8. This network comprises inductance elements I22, I,

' connected similar to inductance elements H0,

and II Land to a variable condenser unit I28, corresponding to condenser H2. Condenser I26 is made, variable so that its impedance may be adjusted to balance precisely transmission line I28. Similarly, line H9 is branched to form a. balanced transmission line I29 through a network comprising inductance elements I23, and I25, and a variable capacity element I 21.

To the outer end of transmission line I 28 is coupled an antenna I30, shown as a dipole antenna, and to line I29 is coupled another dipole antenna I3I. While I have shown antennae I30 and lil as dipoles, it should be distinctly understood that they may be of any desired form so .long as they are designed to form a balanced load. Furthermore, it is clear that instead of leading to antennae, transmission lines I28 and I29 may lead to any desired type of symmetrical load.

If it is desired to use antennae I30 and I3I as a radio beacon, these antennae should be arranged at a suitable angle with respect to each other to assaoie lation in such as to preserve the symmetry of the system. In the arrangement according to Fig. 1, I provide, for modulating the antennae, a filter, comprising resonant quarter wavelength frames I32 and I33 constituting sections of transmission line and loosely coupled to the transmission line. These frames are coupled to the transmission line inductively primarily through capacitive induction and may be precisely tuned by means of trimming condensers I34, i 35. When these frames are properly positioned with respect to the transmission line and accurately tuned, they will operate to substantially stop all of the energy from flowing along the transmission line. Although I have illustrated these tuned coupled sections as open-ended frames, they may have other forms, such as closed frames of proper length or may be of various other formations. For structural details of the various forms of transmission modifying networks, reference may be had to Patent No. 2,159,648, issued May 23, 1939, on an application of Andrew Alford, Ser. No. 162,353 filed September 8, 1937. Sinc the filtering action of coupled transmission line sections, such as shown at I32 and 933 are very critical with tuning, their effect on the flow of energythrough transmission lines I28, E29, may be modified by slightly detuning the section. This fact is made use of in producing the modulation of the energy transmitted to the antennae. Across each of networks I32, I33, I provide split-stator condensers I36, I31. These condensers are arranged with the fixed plates coupled to the separate conductors of the transmission line, while the rotary plates are driven at a uniform rate by means of a motor I40 or other means. Condensers H36 and I3! may be made with a different number oi.

notches in the stator plate so that the energy fiowing along transmission lines I28, i253 is interrupted at a different rat to impress a different modulation upon the energy radiated from antennae I30, I3I.

One form of split-stator condenser suitable for use in the system of Figure l, is illustrated in Figure 2. This condenser comprises fixed toothed stators 2!", 202, connected to the opposite side of a. balanced line 260, and a. single rotary plate element 203. When 203 is rotated at a uniform rate the tuning of the condenser is varied periodically, depending upon the speed of the rotor 203 and the number of teeth on stator plates 2III,-202. Thus a chopping or keying of energy may be accomplished by means of this rotary condenser connected across a tuned frame such as I32. The frequency of modulation may be varied by varying the number of teeth on the con-' denser or by driving the rotors of the condensers at different speeds. The percentage or depth of modulation may be controlled by so choosing the 'thatthe balancing network need not be com-' posed of two induotances and a single capacity as shown, but maybe of any form of impedance so long as they satisfy the requirement specified above.- tances III) and III of I08, equal capacities should be substituted therefor and an inductance. reac- It is thus clear that in place of induc-- Similarly, the impedance element in the network associated with the separate antennae circuit could be of different values if desired without altering the scope of my invention. It should further be understood, according to the general reciprocity theorum, that instead of a transmit ter, the system may constitute a receiving arrangement. Antennae I30, i3! receive radio signals and transmit them over balanced lines to an unbalanced receiver. In Fig. 3, I have il1ustrat d an alternative form of modulating system which may be substituted for that illustrated in Fig. 1. In this arrangement 320, 32!, 3l8 and 3l9, represent the power adjusting condensers and the conductors of the transmission line similar to that disclosed in Fig. 1. Similarly the network comprises inductances 322, 324 and capacity 326, and inductances 323, 325, capacity 326, correspond to similar elements in Fig. 1. Loads 330, 33I, may be antennae corresponding to I30, H! or any other form of symmetrical load. The IroduIatin-g system, however, differs from that shown in Fig. 1. At MI, 342 are illustrated two half-wave length short circuited frames connected at the proper point across balanced transmission lines 328, 329, respectively. At a point midway of the length of transmission line sections 34l, 342 are provided short circuiting switches 343, 344, which are driven by means of a motor 34!). Adjustable short circuiting bars 345, 345, are provided on each of the sections 34!, 342.

This modulating system operates as follows:

When a short circuiting switch 343 is crosswise so as to short circuit the network 34|,-this network forms a short circuited quarter wavelength line connected across transmission line 328. Aside from resistance and radiation losses the circuit will not drain nor hamper flow of energy along transmission line to load 330. When switch 343 is turned to the open position the eilective circuit from the transmission line extends out to the shortcircuited end of the halt-wavelength section 34l. This then constitutes a halfwavelength short circuited filter across the main line preventing substantially all of the energy from flowing to the antenna. Thus the modulation may be obtained by' interrupting the flow of energy along the line by means of the short circuiting switch 343. Similarly modulations may be efiected in the energy of line 329 by short circuiting switch 344. These switches may be pro- .vided with a plurality of segments so as to interrupt the flow at different rates in the two different lines so as to provide'diiierent modulations of the energy for the two loads. If it is desired to utilize less than modulation, short circuiting bars 345, 346 may be changed in position so as to alter the length of the section from that of a full half-wavelength.

While I have described my invention with references to figures illustrating a preferred embodiment thereof, it should be understood that this description is merely by way of illustration and not a limitation of the scope of my invention, which is defined in the accompanying claims.

What I claim is:

1. Radio frequency system including an unbalanced energy source, two push-pull electronic tubes, means for feeding said tubes from said source in symmetry, including, connected between theinput grids of said tubes, two inductances connected adjacent to each grid and a blocking condenser connected between said inductances, so that the direct current potential of said two grids may be independent, 9. second condenser connected from one side of said first condenser to ground, unbalanced feed means extending from said source to ground and directly to one of said grids, and grid biasing means connected respectively to the two sides of said blocking condenser.

2. System according to claim 1, additionally including a variable condenser connected in series between said source and the grid fed directly therefrom, said variable condenser being of a value not influencing the balancing of said system, but acting as a variable power adjusting means.

PAUL F. BYRNE. 

